The water felting of dilute aqueous dispersions of mineral wool and lightweight aggregate is a well-known commercial process for manufacturing acoustical tile or panels. In this process, aqueous slurry of mineral wool, lightweight aggregate, cellulose fiber, binder, and other desired ingredients is flowed onto a moving foraminous support wire, such as that of a Fourdinier or Oliver mat forming machine, for dewatering. The slurry may be first dewatered by gravity and then dewatered by vacuum suction means to form a base mat. The wet base mat is then pressed (with or without the application of additional vacuum) to the desired thickness between rolls and a support wire to remove additional water. The wet base mat is dried in heated convection drying ovens and the dried material is cut to the desired dimensions, fissured and/or perforated to impart acoustical absorbency and optionally face coated, such as with paint, to produce acoustical tiles and panels.
Mineral wool acoustical tiles are necessarily very porous to provide good sound absorption. As taught in U.S. Pat. Nos. 3,498,404; 5,047,120; and 5,558,710, all incorporated herein by reference in their entirety, mineral wool fibers have also been incorporated into the composition to improve sound absorption properties and to provide lightweight acoustical tiles or panels.
U.S. Pat. No. 5,964,934, incorporated herein by reference in its entirety, teaches the use of an expanded perlite, treated with a silicone compound to reduce its water retention, in a furnish of mineral wool, expanded perlite, cellulose fiber, and optionally a secondary binder in a water felting process to produce an acoustical tile product.
Acoustical tile composition must contain a binder, which has typically employed starch. U.S. Pat. Nos. 5,911,818 and 5,964,934, incorporated herein by reference in their entirety, suggest that as much as 15% by weight of the composition may be starch although 6-7% by weight is more normally used.
U.S. Pat. No. 5,250,153, incorporated herein by reference in its entirety, describes the use of latex binders for acoustical tile compositions and a wide variety of latex binders have been suggested for this use.
U.S. Pat. No. 6,855,753, incorporated herein by reference in its entirety, has suggested that a wet-strength resin such as a polyamine epichlorohydrin resin be used to replace conventional starch binder and that the resulting composition may be more efficiently fabricated into acoustical tiles and panels in a water felting process.
US Patent Application Publication Number 2004/209071 A1, incorporated herein by reference in its entirety, discloses a composition for slurry for manufacture of acoustical panels includes one or more fillers, one or more binders, and water and zinc pyrithione.
US Patent Application Publication Number 2005/191465 A1, incorporated herein by reference in its entirety, discloses an abuse-resistant, cast acoustical tile having improved impact resistance and excellent sound absorption values. The acoustical tiles have aggregate particles applied to the surface of a wet pulp in the casting process and the particles are embedded in the pulp by compression with a roll and/or smoothing plates.
Noise reduction coefficient (NRC) is a scale representation of the amount of sound energy absorbed upon striking a particular surface, with a NRC value of 0 indicating perfect reflection and a NRC of 1 representing perfect absorption of sound energy. The NRC value is an average of four sound absorption coefficients of the particular surface at frequencies of 250 HZ, 500 HZ, 1000 HZ, and 2000 HZ, which cover the range of typical human speech. In laboratory test of materials in a laboratory per ASTM C423-17, only the face of the sample is exposed to the sound energy, as would be the case in a typical installation. Under some circumstances NRC's greater than 1 may be obtained, but this is an artifact of the test method due to diffraction/edge to area effects.
The Ceiling Attenuation Class (CAC) rating quantifies how much sound is lost when it is transmitted through the ceiling of one room into an adjacent room through a common plenum. A higher CAC rating indicates that the ceiling system allows less sound transmission. The CAC is measured using the test standard ASTM E 1414-16, in which the sound levels are measured in the source room and an adjacent room.
There have also been attempts to produce a higher NRC product using the water felting process by lowering the stock flow of the composition in an attempt to produce a lower density product, but these attempts only produced a product that had a comparative density to conventional panels but at a reduced product thickness.
U.S. Pat. No. 7,862,687 to Englert discloses an acoustical tile composition with a high NRC of 0.80 to 0.95 achieved only by modifying the production method to eliminate the pressing of the wet base mat and utilize only vacuum for dewatering.